Photosynthesis and respiration of phaeophycean-dominated macroalgal communities in summer and winter

Abstract

This study presents the results of research on the photosynthesis and respiration of a fucoid dominated, macroalgal community in South Australia. We present quantitative measurements of photosynthesis, obtained in situ, using a deployable photorespirometry system. Maximal photosynthetic rates at saturating photon irradiances were the same between summer and winter ( Pm gross = 30 μmol O 2 g −1 wet weight h −1), but there were significant seasonal changes in the dark respiration rate from 4.5 μmol O 2 g −1 wet weight h −1 in summer to 1.5 μmol O 2 g −1 wet weight h −1 in winter. Both the compensation photon irradiance ( Ic) and the subsaturating photon irradiance ( Ik) were higher in summer (33.9 and 214 μmol photons m −2 s −1, respectively) than in winter (8.0 and 149 μmol photons m −2 s −1). Estimates of net 24-h production range from 73 μmol O 2 g −1 wet weight day −1 in winter to 167 μmol O 2 g −1 wet weight day −1 in summer. On an annual basis this represents a net biomass production of 20 kg m −2 from a standing biomass of 3 kg m −2 which results in an annual turnover of around six to seven times the standing biomass.